Patrick Hennessy writes about politics for the Telegraph.

It will take a Brownite to force Gordon Brown out

James Purnell's bombshell resignation last night makes it inevitable Gordon Brown will be forced out. Or does it?

Not necessarily. Purnell insisted he was acting alone – indeed, his move was so secret that even some of his closest aides did not know – and the immediate reaction from the Cabinet's other Blairite ministers seems to bear this out.

David Miliband, crucially, has indicated to the BBC and Sky News that he will not follow Purnell out of the door. John Hutton has said that the former work and pensions secretary made "the wrong decision."

Andy Burnham, perhaps Purnell's closest friend in politics, said: "Gordon Brown is the man to take us through these difficult times."

Of course, Brown still has a nightmare few days ahead but if his team can successfully isolate Purnell, as they did with Hazel Blears, their task will be made fractionally easier. An MP with close links to the PM sent out a text message within minutes of Purnell's resignation labelling the move "anti-party."

For me, it will still take a Brownite to force Brown out. Alistair Darling losing the Chancellorship and quitting the government would be a blow which might prove to be the fatal one.